The proposed work consists of a study of some of the mechanisms that regulate the secretion of ACTH and TSH. Of particular current interest are the hypothalamic and pituitary roles of prostaglandins in this regard. Another major endeavor will concern the side(s) and mechanism(s) of the feedback regulation of TSH secretion by T3 and T4. Finally, several of the interactions between the adrenocortical axis and the thyroid axis are to be studied. Whenever possible, the experiments are performed using unanesthetized, unstressed animals. A central theme of this work is to study these endocrine systems as dynamic systems, in that we will be examining time courses of responses rather than single points in time. Fluorometric and radioimmunoassays are used in conjunction with stereotoxic microinjection of hypothalamus or anterior pituitary and chronic catheterization techniques.